The proposed work is a detailed analysis of amino acid metabolism by muscle in intact man. The forearm technique is utilized by which muscle uptake and release of various metabolites, including amino acids can be quantified. In the work currently in progress, alpha-keto derivatives of essential amino acids are infused into the brachial artery, and measurements made of their effects on forearm blood flow, and on the balance of glucose, lactate, and amino acids across forearm muscles. It is hoped by these studies to quantify the consumption of keto-acids by muscle, to measure their conversion by transamination to the corresponding essential amino acids, and to identify the sources of amino nitrogen required for this conversion. It is also hoped to determine whether the provision of alpha-keto derivatives of amino acids have an anabolic effect on muscle protein. This is important because they are potential dietary substitutes for amino acids in patients with diseases impairing the ability to detoxify and excrete nitrogen. Bibliographic references: Sapir, D.G., O.E. Owen, T. Pozefsky, and M. Walser. Nitrogen sparing induced by a mixture of essential amino acids given chiefly as their keto-analogues during prolonged starvation in obese subjects. J. Clin. Invest. 54:974, 1974; Smith, S.R., P.J. Edgar, and T. Pozefsky. Insulin secretion and glucose tolerance in adults with protein-calorie malnutrition. Diabetes 24:444, 1975.